A solar power tower is a power plant that converts solar thermal energy into electrical energy for connection to a utility grid. It can be sized to produce a wide range of power for commercial use from about 1 MWe to about 200 MWe.
The sun's thermal energy is intercepted by a collector system that is comprised of thousands of sun tracking mirrors called heliostats. This energy is redirected and concentrated on a heat exchanger, called a solar receiver, typically mounted on a tall tower. The receiver includes a plurality of solar receiver panels positioned around an outside wall of the receiver. Each solar receiver panel includes a plurality of receiver tubes through which a heat transfer fluid, or coolant, flows. Typically, the coolant is molten salt, but the coolant can be any other suitable heat transfer fluid, for example a liquid metal such as sodium (Na) or a mixture of sodium (Na) and potassium (K), water or steam. The coolant is heated by the redirected solar energy as it flows up through the receiver tubes of one receiver panel and down through the receiver tubes of the next receiver panel until it has been circulated through all the solar receiver panels, at which point the coolant exits to the hot thermal storage tank. The heated coolant is stored in the hot tank until it is pumped to a steam generator where the heat from the coolant is used to generate steam which drives a turbine/generator device to create electricity.
To avoid damage to the receiver tubes, monitoring the coolant temperature in the receiver tubes is critical to the operation of the solar receiver. Typically, a plurality of thermocouples are sporadically tack welded to the back side of various receiver tubes and receiver panel headers throughout the solar receiver. The thermocouples transmit discrete signals to a system processor such that the temperature at specific locations on various receiver tubes can be monitored. To obtain comprehensive temperature data for the entire length of every receiver tube would require a multiplicity of thermocouples tack welded to each receiver tube. This would be very labor intensive and costly. Additionally, over time, due to the expansion and contraction of the receiver tubes, caused by the heating and cooling of each tube, the thermocouples and the leads connecting the thermocouples to the system processor would be susceptible to damage. Replacing broken or damaged thermocouples or thermocouple leads would also be very labor intensive and costly.
Furthermore, having thermocouples sporadically placed throughout each receiver panel allows the potential for damage to the receiver tubes. When the thermocouples are sporadically placed throughout the receiver panel, some receiver tubes may have thermocouples attached while an adjacent tube may not. Thus, the coolant temperature in the tube without the thermocouple is only assumed to be approximately the same as the temperature of the coolant in the adjacent tube that has a thermocouple attached thereto. If there is flow blockage in a tube without the thermocouple there will be no temperature indication of the blockage. Thus, the tube may overheat and rupture causing time consuming and expensive repairs.
At night, or anytime sun light is not available, some coolants such as molten salt and liquid metals must be drained from the receiver to a cold thermal storage tank to avoid the coolant from freezing in the receiver tubes, which could cause damage to the tubes. Thus, when the sun light becomes available, the coolant must be pumped from the cold thermal storage tank to the receiver. To avoid thermally shocking the receiver tubes, which can cause damage to the tubes, the entire solar receiver must be preheated. Infrared (IR) cameras have been used to determine when the entire solar receiver has been preheated to the proper temperature. Known applications of IR cameras typically utilize 1 IR camera for gross evaluation of part of the surface temperature of the solar receiver. Prior to filling the solar receiver, one or more regions of the solar receiver would be evaluated using the IR camera to determine whether the temperature of the solar receiver is uniform and at a suitable temperature. Known solar power tower systems have utilized a single IR camera for the limited purpose of gross evaluation of a portion of the surface temperature of the solar receiver prior to filling the solar receiver. Subsequent to filling the solar receiver, evaluation of the temperature of the coolant flowing through the receiver tubes of each solar panel is typically evaluated using the sporadically placed thermocouples.
Therefore, it would be highly desirable to be able to obtain comprehensive temperature data for the entire length of each receiver tube of each receiver panel in the solar receiver. Additionally, it would be desirable to do so without using thermocouples, thereby reducing the labor and cost associated with the use of thermocouples as described above.